The objective of this research is to define the molecular-biochemical mechanism of how avian oncornavirus replicate and interact with cells. Specifically, we will study the relationship between the structure of viral RNA and its capacity to be translated into viral proteins. Three viral specific mRNAs including genome length 34S RNA, 28S and 21S RNA species have been identified in extracts of ASV-infected cells. The origin of these smaller ASV-specific mRNAs is as yet unknown. These studies will test the hypothesis that viral 34S RNA is processed into the smaller mRNAs by action of RNase III (purified from duck embryo or E. coli cells). The coding capacity of in vitro produced fragments will be determined by translation in a cell-free protein synthesizing system and by hybridization to specific viral cDNA probes. Furthermore, the above enzymes will be tested for the presence of RNA ligase activity in order to determine if either enzyme could catalyze the transfer of 5' terminus 34S RNA sequences to smaller mRNAs in vitro. RNA leader sequences containing the 5' RNA terminus have been shown to be present on 28S and 21S RNA species. Finally, evidence from this laboratory has shown that viral protein p19 binds to 34S RNA at RNase III sensitive sites suggesting that this protein may act as a control element in processing of viral RNA. In order to test this hypothesis, we will analyze the type and amount of ASV-specific mRNAs present in cells infected with avian oncornavirus in which we have shown p19 proteins to be altered.